The present invention relates to a method and a device for draining liquid from a secondary separator connected to the high pressure end of a liquid injected compressor.
In a prior known embodiment involving of such separation, the liquid is driven from the bottom of the secondary separator by the pressure in the separator through a drainage conduit directly to the inlet opening of the compressor. During operation of the compressor, the amount of liquid which is to be drained sometimes is small, which causes a comparatively large gas flow in the drainage conduit. Since this gas flow is reexpanded to the inlet pressure of the compressor, the efficiency of the compressor is decreased because the energy used to compress the gas cannot be utilized by the compressor. Furthermore, the gas volume increases considerably during its reexpansion, resulting in a considerable decrease of the amount of fresh gas supplied to the compressor during the suction phase. A further disadvantage is that when the compressor is not operating the liquid is driven into the compressor. Thus, when the compressor is restarted, a certain amount of liquid remains in the compression chamber, which may cause starting problems, particularly at low temperatures when the viscosity of the liquid is high.